Formation of heterotopic metallacalix[n] arenes (n=3, 4, 6) containing ethylenediaminepalladium(II) metal fragments and 4,7-phenanthroline and 2-pyrimidinolate bridges.: Synthesis, structure and host-guest chemistry

A multicomponent reaction involving ethylenediaminepalladium(II), 2-pyrimidinol derivatives (L) [L=2-pyrimidinol (a); 4-methyl-2-pyrimidinol(b); 4,6-dimethyl-2-pyrimidinol (c)] and 4,7-phenanthroline(4,7-phen) leads to the formation of heterotopic cyclic metallamacrocycles of the type [Pd-n(en)(n)(mu-N,N'-L)(m)(mu-N, N'-4,7-phen)(n-m)]((2n-m)+) [n=3, m=1 (3); n=4, m=2 (4); n=6, m=4 (5)]. These species can be obtained by different reaction pathways, including: (i) reaction of ethylene diaminepalladium(II), L and 4,7-phen building blocks and (ii) reaction of the homotopic species [Pd-4(en)(4)(mu-N, N'-L)(4)](4+) (1) and [Pd-3(en)(3)(mu-N, N'-4,7-phen)(3)](6+) (2). The resulting heterotopic metallamacrocycles have been characterised by 1D and 2D H-1 NMR spectroscopy. Additionally, species 3c and 4a have been studied by X-ray crystallography. The former one contains almost isosceles triangles of [Pd-3(en)(3)(mu-N, N'-4,6-dimethyl-2-pyrimidinolate)(mu-N, N'-4,7-phen)(2)](5+) formulation, exhibiting a pinched-cone conformation. 4a contains a tetranuclear parallelogram [Pd-4(en)(4)(mu-N, N'-2-pyrimidinolate)(2)(mu-N, N'-4,7-phenanthroline)(2)](6+), exhibiting a 1,3-alternate conformation. The host-guest properties of the here reported species have been studied, showing that they are able to interact with cationic as well as with anionic species.